Haptic actuator including pulse width modulated waveform based movement for overcoming resting inertia and related methods

ABSTRACT

A haptic actuator may include a housing, at least one coil carried by the housing, a field member movable within the housing responsive to the at least one coil, and at least one mechanical limit stop between the housing and the field member. The haptic actuator may also include circuitry capable of generating a pulse width modulated (PWM) waveform for the at least one coil to move the field member from an initial at-rest position and without contacting the at least one mechanical limit stop.

TECHNICAL FIELD

The present disclosure relates to the field of electronics, and, moreparticularly, to the field of haptics.

BACKGROUND

Haptic technology is becoming a more popular way of conveyinginformation to a user. Haptic technology, which may simply be referredto as haptics, is a tactile feedback based technology that stimulates auser's sense of touch by imparting relative amounts of force to theuser.

A haptic device or haptic actuator is an example of a device thatprovides the tactile feedback to the user. In particular, the hapticdevice or actuator may apply relative amounts of force to a user throughactuation of a mass that is part of the haptic device. Through variousforms of tactile feedback, for example, generated relatively long andshort bursts of force or vibrations, information may be conveyed to theuser.

SUMMARY

A haptic actuator may include a housing, at least one coil carried bythe housing, and a field member movable within the housing responsive tothe at least one coil. The haptic actuator may also include at least onemechanical limit stop between the housing and the field member andcircuitry capable of generating a pulse width modulated (PWM) waveformfor the at least one coil to move the field member from an initialat-rest position and without contacting the at least one mechanicallimit stop. Accordingly, the field member may move, for example, from aninitial at-rest position to a steady state operation, without contactingthe mechanical limit stop.

The PWM waveform may have a pulse width that decreases over time for anumber of pulses. The PWM waveform may have a constant pulse width afterthe number of pulses, for example.

The PWM waveform may have a decreasing amplitude for a number of pulses.The PWM waveform may have a constant amplitude after the number ofpulses, for example.

The PWM waveform may be a bipolar waveform, for example. The PWMwaveform may have a constant repetition rate. The housing, at least onecoil, and field member may define a resonant frequency, and therepetition rate may be at an integer multiple of the resonant frequency,for example.

The circuitry may include an intermediate waveform generator capable ofgenerating a bipolar square wave and a low pass filter coupled to theintermediate waveform generator. The intermediate waveform generator maybe capable of generating an intermediate waveform based upon anexponential function, for example.

An electronic device aspect is directed to an electronic device that mayinclude a device housing and wireless communications circuitry carriedby the device housing. The electronic device may also include a hapticactuator carried by the device housing. The haptic actuator may includean actuator housing, at least one coil carried by the actuator housing,and a field member movable within the actuator housing responsive to theat least one coil. The haptic actuator may also include at least onemechanical limit stop between the actuator housing and the field member,and circuitry capable of generating a pulse width modulated (PWM)waveform for the at least one coil to move the field member from aninitial at-rest position and without contacting the at least onemechanical limit stop. The electronic device may also include acontroller coupled to the wireless communications circuitry and thehaptic actuator, and capable of performing at least one wirelesscommunication function and selectively operating the haptic actuator.

A method aspect is directed to a method of operating a haptic actuatorthat may include a housing, at least one coil carried by the housing, afield member movable within the housing responsive to the at least onecoil, and at least one mechanical limit stop between the housing and thefield member. The method may include using circuitry to generate a pulsewidth modulated (PWM) waveform for the at least one coil to move thefield member from an initial at-rest position and without contacting theat least one mechanical limit stop.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an electronic device including a hapticactuator according to an embodiment of the present invention.

FIG. 2 is a schematic block diagram of the electronic device of FIG. 1.

FIG. 3 is a more detailed schematic diagram of the haptic actuator ofFIG. 1.

FIG. 4 is a graph of waveforms generated by the circuitry of the hapticactuator of FIG. 3.

FIG. 5 is a graph illustrating momentum versus voltage for puresinusoidal input waveform and a PWM waveform output by the circuitry ofthe haptic actuator of FIG. 3.

FIG. 6 is a schematic diagram of a haptic actuator according to anotherembodiment.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout and prime notation is used todescribe like elements in different embodiments.

Referring initially to FIGS. 1 and 2, an electronic device 20illustratively includes a device housing 21 and a controller 22 carriedby the device housing. The electronic device 20 is illustratively amobile wireless communications device, for example, a wearable wirelesscommunications device, and includes a band 28 or strap for securing itto a user. The electronic device 20 may be another type of electronicdevice, for example, a cellular telephone, a tablet computer, a laptopcomputer, etc.

Wireless communications circuitry 25 (e.g. cellular, WLAN Bluetooth,etc.) is also carried within the device housing 21 and coupled to thecontroller 22. The wireless communications circuitry 25 cooperates withthe controller 22 to perform at least one wireless communicationsfunction, for example, for voice and/or data. In some embodiments, theelectronic device 20 may not include wireless communications circuitry25.

A display 23 is also carried by the device housing 21 and is coupled tothe controller 22. The display 23 may be a liquid crystal display (LCD),for example, or may be another type of display, as will be appreciatedby those skilled in the art.

Finger-operated user input devices 24 a, 24 b, illustratively in theform of a pushbutton switch and a rotary dial are also carried by thedevice housing 21 and is coupled to the controller 22. The pushbuttonswitch 24 a and the rotary dial 24 b cooperate with the controller 22 toperform a device function in response to operation thereof. For example,a device function may include a powering on or off of the electronicdevice 20, initiating communication via the wireless communicationscircuitry 25, and/or performing a menu function.

The electronic device 20 illustratively includes a haptic actuator 40.The haptic actuator 40 is coupled to the controller 22 and provideshaptic feedback to the user in the form of relatively long and shortvibrations or “taps”, particularly when the user is wearing theelectronic device 20. The vibrations may be indicative of a messagereceived, and the duration of the vibration may be indicative of thetype of message received. Of course, the vibrations may be indicative ofor convey other types of information. More particularly, the controller22 applies a voltage to move a moveable body or masses between first andsecond positions.

While a controller 22 is described, it should be understood that thecontroller 22 may include one or more of a processor and other circuitryto perform the functions described herein.

Referring now additionally to FIG. 3, the haptic actuator 40 includes ahousing 41 and a coil 44 carried by the housing. Of course, there may bemore than one coil carried by the housing 41.

A field member 50 is movable within the housing 41 responsive the coil44. The movement of the field member 50 creates the haptic feedback, ortapping, as will be appreciated by those skilled in the art. While themovement of the field member 50 may be described as being moveable inone direction, i.e., a linear haptic actuator, it should be understoodthat in some embodiments, the field member may be movable in otherdirections, i.e., an angular haptic actuator, or may be a combination ofboth a linear and an angular haptic actuator.

The field member 50 may include one or more masses and may be shaped fora particular application or operation. The field member 50 may alsoinclude one or more permanent magnets cooperating with the coil 44 toprovide movement of the field member. The field member 50 may alsoinclude a suspension system that may include one or more springs formaintaining the field member suspended in the housing 41. The springsmay include mechanical springs, such as, for example, coil springs, leafsprings, and flexures. The springs may also or additionally includemagnetic springs that, through interaction with the permanent magnetsand/or ferritic parts of the housing 41, if any, store and amplify theenergy in the form of elastic/magnetic energy. In addition, thesuspension system, for example, through shafts, linear/angular bearings,sliding bearings, flexures, multi-bar linkage mechanisms, and springs,may enable motion of the field member 50 in the desired direction (e.g.X axis in a linear actuator or around a certain axis in an angularactuator) while constraining motion in other degrees of freedom. Thesuspension system may include other and/or additional components formaintaining the suspension of the field member 50 as well as constrainmovement of the field member.

The haptic actuator 40 also includes mechanical limit stops 45 a, 45 bbetween the housing 41 and the field member 50. The mechanical limitstops 45 a, 45 b limit the movement of the field member to a desiredrange and/or stop the field member from crashing or banging into thehousing 41. While mechanical stops 45 a, 45 b are described, it will beappreciated that the mechanical stops may be part of or a portion of thehousing 41.

Typically, circuitry generates a sinusoidal drive waveform that drivesthe field member to move from an initial at-rest position. However, aswill be appreciated by those skilled in the art, in a stationary orat-rest position, the field member 50 has a static friction associatedwith it which may cause the field member to “get stuck” despite theapplication of a drive voltage. A certain amount of force or voltage isthus needed to overcome this static friction force t cause the fieldmember 50 to move. One approach to drive the field member 50 from theat-rest position is to increase the drive voltage or amplitude of thesinusoidal drive waveform. However, once the static friction force isovercome, the field member 50 typically rapidly accelerates and crashesor bangs into the mechanical limit stops 45 a, 45 b.

In some applications it may be particularly desirable to not have thefield member 50 hit or bang into the mechanical limit stops 45 a, 45 bas this may generate a corresponding “banging” noise. To reduce theamount of noise, for example, caused by the increased amplitude, thehaptic actuator 40 includes circuitry 51 that generates a pulse widthmodulated (PWM) waveform for the coil 44 to move the field member 50without contacting the mechanical limit stops 45 a, 45 b.

Referring now additionally to the graph 60 in FIG. 4, instead of using asinusoidal waveform to drive the field member 50, the circuitry 51generates a PWM waveform based upon a sinusoidal input waveform. The PWMwaveform is generated to have certain characteristics that may beparticularly beneficial to the “sticking” of the field member 50described above.

In particular, the circuitry 51 generates a bipolar PWM waveform to havea pulse width that decreases over time for a number of pulses and has aconstant pulse width after the number of pulses. The number of pulsesmay be any number of pulses and may be based upon desired operatingcharacteristics, for example, duration and/or type of the hapticfeedback, and/or mechanical characteristics of the haptic actuator 40.As will be appreciated by those skilled in the art, the adaptive dutycycle may be more robust with respect to “sticky” haptic actuators, forexample, haptic actuators having a relatively high Q-factor value.

The circuitry 51 also generates the PWM waveform at a constantrepetition rate or frequency. As will be appreciated by those skilled inthe art, the actuator housing 41, the coil 44, and field member 50define a resonant frequency. The constant repetition rate may be aninteger multiple of the resonant frequency, for example, to provideincreased field member movement for a reduced amount of energy.

The circuitry 51 includes an intermediate waveform generator 52 thatgenerates a bipolar square wave 61. The bipolar square wave 61 has thePWM waveform characteristics described above. The circuitry 51 alsoincludes a low pass filter 53 coupled to the intermediate waveformgenerator 52. The low pass filter 53 may be desirable to reduce therelatively sharp edges of the bipolar square wave 61. The low passfilter 53 may be a double-sided low pass filter, for example, 500 Hz-1kHz.

The low pass filtered bipolar square wave is illustrated by the line 62and may be referred to as the drive PWM waveform. Illustratively, thecircuitry 51 generates the drive PWM waveform 62 to have a decreasingamplitude for a number of pulses and a constant amplitude after thenumber of pulses. The number of pulses may be any number of pulses andmay be based upon desired operating characteristics, for example,duration and/or type of the haptic feedback, and/or mechanicalcharacteristics of the haptic actuator. As will be appreciated by thoseskilled in the art, the amplitude may be constant after the number ofpulses as the haptic actuator, or more particularly, the field member 50may be at a steady state. Thus, just enough energy or amplitude may beused to maintain the steady state operation.

The threshold or number of pulses that are decreasing in amplitudebefore generating constant amplitude pulses may be determined based uponan exponential function, for example to reduce the chances of or toavoid an overshoot and hitting the mechanical limit stops 45 a, 45 b.For example, if the drive PWM waveform 62 is to be above the threshold,the circuitry 51 may use the threshold limit or constant amplitude ofthe intermediate waveform 62. If however, the drive PWM waveform 62 isto be below the threshold, the drive PWM waveform may have a respectiveamplitude (either decreasing or constant) so long as it is below thethreshold.

To generate the drive PWM waveform 62 from a sinusoidal input, thecircuitry 51, in some embodiments, may apply an algorithm. The algorithmmay be embodied using hardware or by software, firmware, etc. loadedinto a memory and executed by the circuitry. An exemplary algorithm maybe coded as:LPF=tf(1,[½*pi*750)1]);W=V_Vibe*sign(sin(2pi*f0*T))·*(abs(sin(2*pi*f0*T))>(0.95−exp(−2*pi*f0*T/5)));andWF=(lsim(LPF,W,T)+flip(lsim(LPF,flip(W),T))/2)wherein LPF is the function for determining the parameters of the lowpass filter. The “750” is the LPF frequency in this example. The term“(0.95−exp(−2*pi*f0*T/5))” determines how fast the circuitry 51 willgenerate the decreasing pulse widths to the steady state, i.e. thenumber of pulses and/or steady state threshold. The threshold is set bythe exponential term, “0.95−exp.” f0 is the frequency of operation and Tis time. Those skilled in the art will recognize that other terms in thealgorithm are names given to programming functions.

The drive PWM waveform 62 may be considered, relative to a typicalsinusoidal input, a short duty high voltage PWM waveform smoothed by thelow pass filter. As a result of the drive PWM waveform, theelectromotive force is, as opposed to the typical sinusoidal input andwhich is based upon, and more particularly, proportional to the current,may be much larger than the friction force. Thus, the field member 50may not “get stuck” or the static friction forces may be manageable suchthat the field member does not crash or bang into the mechanical limitstops 45 a, 45 b. Additionally, considering the relatively short dutycycle of the drive PWM waveform, the amplitude that causes the movementof the field member 50 or the vibration may be significantly reduced toa manageable and desired level.

Referring now additionally to the graph 70 in FIG. 5 a purely sinusoidalwaveform is illustrated by the line 71 showing momentum versus an amountof applied voltage. The drive PWM waveform generated by the circuitry 51is illustrated by the line 72. Illustratively, the purely sinusoidalwaveform 71 may be particularly undesirable as it may cause “crashing”as a result of the spike in momentum.

While both a controller 22 circuitry 51 of the haptic actuator 40 haverespectively been described herein with respect to their functionality,it will be appreciated by those skilled in the art that the circuitryand the controller may be physically embodied on a single physical chip,for example.

A method aspect is directed to a method of operating a haptic actuator40 that includes a housing 41, at least one coil 44 carried by thehousing, a field member 50 movable within the housing responsive to theat least one coil, and at least one mechanical limit stop 45 a, 45 bbetween the housing and the field member. The method includes usingcircuitry 51 to generate a pulse width modulated (PWM) waveform for theat least one coil 44 to move the field member 50 from an initial at-restposition and without contacting the at least one mechanical limit stop45 a, 45 b.

Referring now to FIG. 6, in another embodiment, the haptic actuator 40′may include a permanent magnet 47′ carried by the housing 41′, and thefield member 50′ may include one or more coils that cooperate with thepermanent magnet. In other words, in contrast to the embodimentdescribed above, the permanent magnet is stationary (i.e., carried bythe housing 41′) and the coils, as part of the field member 50′ aremoving (i.e., connected to the mass). Of course, there may be any numberof coils and/or permanent magnets.

Many modifications and other embodiments of the invention will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is understood that the invention is not to be limited tothe specific embodiments disclosed, and that modifications andembodiments are intended to be included within the scope of the appendedclaims.

That which is claimed is:
 1. A haptic actuator comprising: a housing; atleast one coil carried by the housing; a field member having a restinginertia associated therewith and movable laterally along a path oftravel within the housing responsive to the at least one coil; at leastone mechanical limit stop between the housing and the field member; andcircuitry configured to generate a pulse width modulated (PWM) waveformfor the at least one coil to move the field member laterally along thepath of travel from an initial at-rest position and without contactingthe at least one mechanical limit stop, the PWM waveform having adecreasing amplitude for a number of pulses to overcome the restinginertia and a non-zero constant amplitude thereafter as the field membermoves laterally along the path of travel.
 2. The haptic actuator ofclaim 1 wherein the PWM waveform has a pulse width that decreases overtime for the number of pulses.
 3. The haptic actuator of claim 2 whereinthe PWM waveform has a constant pulse width after the number of pulses.4. The haptic actuator of claim 1 wherein the PWM waveform is a bipolarwaveform.
 5. The haptic actuator of claim 1 wherein the PWM waveform hasa constant repetition rate.
 6. The haptic actuator of claim 5 whereinthe housing, at least one coil, and field member define a resonantfrequency; and wherein the constant repetition rate is at an integermultiple of the resonant frequency.
 7. The haptic actuator of claim 1wherein the circuitry comprises: an intermediate waveform generatorcapable of generating a bipolar square wave; and a low pass filtercoupled to the intermediate waveform generator.
 8. The haptic actuatorof claim 7 wherein the intermediate waveform generator is capable ofgenerating an intermediate waveform based upon an exponential function.9. The haptic actuator of claim 1 wherein the field member has a staticfriction associated therewith; and wherein the PWM waveform has thedecreasing amplitude for the number of pulses to overcome the staticfriction.
 10. An electronic device comprising: a device housing;wireless communications circuitry carried by the device housing; ahaptic actuator carried by the device housing and comprising an actuatorhousing, at least one coil carried by the actuator housing, a fieldmember having a resting inertia associated therewith and movablelaterally along a path of travel within the actuator housing responsiveto the at least one coil, at least one mechanical limit stop between theactuator housing and the field member, and circuitry configured togenerate a pulse width modulated (PWM) waveform for the at least onecoil to move the field member laterally along the path of travel from aninitial at-rest position and without contacting the at least onemechanical limit stop, the PWM waveform having a decreasing amplitudefor a number of pulses to overcome the resting inertia and a non-zeroconstant amplitude thereafter as the field member moves along the pathof travel; and a controller coupled to the wireless communicationscircuitry and the haptic actuator, and configured to perform at leastone wireless communication function and selectively operating the hapticactuator.
 11. The electronic device of claim 10 wherein the PWM waveformhas a pulse width that decreases over time for the number of pulses. 12.The electronic device of claim 11 wherein the PWM waveform has aconstant pulse width after the number of pulses.
 13. The electronicdevice of claim 10 wherein the PWM waveform is a bipolar waveform. 14.The electronic device of claim 10 wherein the PWM waveform has aconstant repetition rate.
 15. The electronic device of claim 14 whereinthe housing, at least one coil, and field member define a resonantfrequency; and wherein the constant repetition rate is at an integermultiple of the resonant frequency.
 16. The electronic device of claim10 wherein the field member has a static friction associated therewith;and wherein the PWM waveform has the decreasing amplitude for the numberof pulses to overcome the static friction.
 17. A method of operating ahaptic actuator comprising a housing, at least one coil carried by thehousing, a field member having a resting inertia associated therewithand movable laterally along a path of travel within the housingresponsive to the at least one coil, and at least one mechanical limitstop between the housing and the field member, the method comprising:using circuitry to generate a pulse width modulated (PWM) waveform forthe at least one coil to move the field member laterally along the pathof travel from an initial at-rest position and without contacting the atleast one mechanical limit stop, the PWM waveform being generated tohave a decreasing amplitude for a number of pulses to overcome theresting inertia and a non-zero constant amplitude thereafter as thefield member moves along the path of travel.
 18. The method of claim 17wherein the circuitry generates the PWM waveform to have a pulse widththat decreases over time for the number of pulses.
 19. The method ofclaim 18 wherein the circuitry generates the PWM waveform to have aconstant pulse width after the number of pulses.
 20. The method of claim17 wherein the circuitry generates the PWM waveform as a bipolarwaveform.
 21. The method of claim 17 wherein the circuitry generates thePWM waveform to have a constant repetition rate.
 22. The method of claim21 wherein the housing, at least one coil, and field member define aresonant frequency; and wherein the constant repetition rate is at aninteger multiple of the resonant frequency.
 23. The method of claim 17wherein the field member has a static friction associated therewith; andwherein the PWM waveform has the decreasing amplitude for the number ofpulses to overcome the static friction.